This invention provides an improved method for fabricating magnetic shielding for critical electronic components which are sensitive to stray magnetic fields.
In the prior art, the usual method of protecting critical electronic components that are sensitive to stray magnetic fields is to shield these components with an enclosure comprising high magnetically permeable or conductive material, such as mu-metal. These enclosures may be fabricated by deep drawing. This technique requires expensive equipment and tooling and results in an enclosure that has large corner and edge radii. For instance, see the housing depicted in U.S. Pat. No. 3,931,618. Still another technique is to cut and fold into a box a single sheet of the high magnetic conductive shielding material. To prevent magnetic leakage at the corners and edges of the box, they are usually welded along the seams and corner. In this process, the magnetic shielding properties of the shielding material is greatly distorted and degraded by the welding. Furthermore, welding is a costly process.
The apparatus fabricated by the method in accordance with the invention overcomes these problems in the prior art. The apparatus comprises overlapping sheets of shielding material to provide an essentially gapless enclosure without welding. At least one sheet overlaps each other opening or abutment of the sheets above or below it. Furthermore, the corners and edges are formed sharply. As a result, the enclosure is a closely and tightly fitting shield. For providing better mechanical stability, the overlapping sheets can be mutually attached by spot welds. Therefore, the shielding material is substantially undegraded as it would be with more extensive welding. And because of the overlapping layers, superior shielding property is realized especially when the shielded component is confronted with a strong field which must be reduced to a minimum value. A common solution in such cases is to use a double-layered shield.